Action Points

Air pollution may increase the risk of insulin resistance in children.

Point out that the relationship doesn't imply causality between air pollution and insulin resistance in children.

Air pollution may increase the risk of insulin resistance in children, German researchers found.

In a large cohort study, insulin resistance increased by 17% for every two standard-deviation increases in nitrogen dioxide (NO2) in the environment and by 18.7% for every two standard-deviation increase in particulate matter-10 (PM-10), Joachim Heinrich, of the German Research Center for Environmental Health, and colleagues reported online in Diabetologia.

"To our knowledge, this is the first prospective study that investigated the relationship of long-term traffic-related air pollution and insulin resistance in children," Heinrich said in a statement. "Insulin resistance levels tended to increase with increasing air pollution exposure, and this observation remained robust after adjustment for several confounding factors, including socioeconomic status, BMI, and passive smoking."

Mark Vanderwel, MD, a pediatric endocrinologist with the Carolinas HealthCare System, who was not involved in the study, warned that the relationship doesn't imply causality.

"Just because there is a link between air pollution levels and the place of birth of these German children and a measure of insulin resistance at age 10 doesn't mean air pollution causes insulin resistance at age 10," Vanderwel told MedPage Today. "It just means that this German study has shown that there is a relationship between the two."

Epidemiological studies looking at associations between air pollution and type 2 diabetes haven't been consistent, particularly for adults, and studies on insulin resistance are scarce, the researchers said.

To investigate potential links between insulin resistance and air pollution in children, Heinrich and colleagues took fasting blood samples from 397 children -- 10-year-olds who didn't have diabetes -- who were enrolled in two prospective German birth cohort studies.

One cohort lived in Munich in South Germany, the other in Wesel in West Germany. Sources of pollution in Wesel are from industry, long-range transportation, and local mobile traffic, while pollution in Munich is dominated by local traffic exhaust.

The researchers used land-use regression models to assess exposure to traffic-related air pollution, and assessed insulin resistance via the homeostatic model assessment of insulin resistance (HOMA-IR).

Overall, they found that levels of insulin resistance were higher in children with greater exposure to air pollution.

Specifically, insulin resistance rose by 17% for every two standard-deviation increases in ambient NO2 and by 18.7% for every two standard-deviation increases in PM-10, they reported.

Heinrich and colleagues also discovered that proximity to the nearest major road increased insulin resistance by 7.2% per 500 meters.

They hypothesized that since air pollution can increase oxidative stress and inflammation, this mechanism may be behind a link to insulin resistance, though they noted that their study could not prove causality.

"Although toxicity differs between air pollutants, they are all considered potent oxidisers that act either directly on lipids and proteins or indirectly through the activation of intracellular oxidant pathways," Heinrich said in the statement. "In addition, some studies have reported that short-term and long-term increases in particulate matter and nitrogen dioxide exposure lead to elevated inflammatory biomarkers, another potential mechanism for insulin resistance."

The study was also limited by the potential for exposure misclassification, the researchers warned.

Heinrich said he and his colleagues are currently investigating moving from a polluted area to a clean one, or vice versa, in order to "explore the persistence of the effect related to perinatal exposure and to evaluate the impact of exposure to increased air pollution concentration later in life."

He cautioned that it is still unclear whether this early link between insulin resistance and air pollution has any clinical relevance, but the results "support the notion that the development of diabetes in adults might have its origin in early life including environmental exposures."

The study was supported by the German Federal Ministry of Education and Research.

The researchers reported no conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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